The present invention relates to a speed reducer with rotation detector, and more particularly to a speed reducer with rotation detector for use with a motor, in which the data of output rotation can be fed back to the motor to drive correctly a joint of an industrial robot.
Conventionally, in a FA (Factory Automation) field, various speed reducers have been used for the precision control of industrial robots, machine tools, and dividing plates. These speed reducers may include, for example, a harmonic drive (Registered Trademark) speed reducer and other reducers. A speed reducer can be used with a motor to reduce the rotation of the motor, and drive an industrial robot. In this case, in order to drive a joint of the industrial robot correctly, a so-called semi-closed control method has been well-known in which the rotational information input from the motor to the speed reducer is detected, and the rotation of the motor is controlled on the basis of that information.
However, in such semi-closed control method, the output rotation of the speed reducer is predicted from the rotational information input from the motor to the speed reducer to control the rotation of the motor. However, in this semi-closed control method, there was some limit in the control precision of the rotation of the motor because it might be susceptible to a mechanical error of a speed reducing mechanism.
One method to resolve this problem, as disclosed in JP-A-8-184349, relied on a so-called full-closed control in which the rotational information output from an eccentric oscillating speed reducer is detected to control the rotation of the motor, based on its information. With this full-closed control method, the rotation of the motor can be controlled in accordance with the rotational information output from the eccentric oscillating speed reducer, viz., the rotational information in the neighborhood of a control object, resulting in less mechanical error of the speed reducing mechanism, and higher control accuracy than the method using the semi-closed control.
However, in the method as disclosed in JP-A-8-184349 as above cite, means for detecting the rotational information output from the eccentric oscillating speed reducer and outputting its information to the outside (hereinafter referred to as a rotation detector) was constituted of a code plate and a sensor. Hence, the rotation detector was restricted in resolving power by the code plate.
One technique to make better the resolving power of the rotation detector was the use of a multiplier for multiplying the frequency of the code plate by processing the information output from the rotation detector. The information output from the rotation detector is passed as an electric signal to the multiplier, its electric signal has a very low voltage level, and is susceptible to noise, resulting in lower precision of the rotation detector.
It is an object of the present invention to provide a speed reducer with rotation detector which can detect the output rotation at high resolving power and high precision, and make the full-closed control of a motor at high resolving power and high precision by using this speed reducer with rotation detector.
In order to solve the above problem, the present invention provides the following preferable arrangements:
(1) A speed reducer with rotation detector has an input shaft for inputting the rotation, a first shaft in co-axial relation with the input shaft, a second shaft in co-axial relation with the first shaft and forming a space with the first shaft to surround one end portion of the first shaft, bearings interposed between the first shaft and the second shaft to be in co-axial relation with each other, one being supported rotatably by the other, a speed reducing mechanism for reducing the rate of rotation input into the input shaft when one of the first shaft and the second shaft is fixed, to output it to the other of the first shaft and the second shaft, and a rotation detector for detecting the rotational information of one of the first shaft and the second shaft with respect to the other, interposed within the space formed between the first shaft and the second shaft. The rotation detector comprises a code plate having the positional information corresponding to the rotation, a detecting portion for detecting the positional information of the code plate to output an electrical signal into which the positional information is transformed, and an electronic device having amplifying means for amplifying a voltage of the electrical signal output from the detecting portion. Hence, an electric signal output from the detecting portion has a voltage level amplified by the electronic device in the neighborhood of the detecting portion, making it possible to reduce the influence of noise from the outside. Therefore, the rotational information of one of the first shaft and the second shaft with respect to the other can be captured accurately. Accordingly, if the speed reducer with rotation detector according to the invention is used with a motor, the rotational information output from the speed reducer with rotation detector can be detected. Thus, the rotation of the motor can be controlled at high precision, based on its information.
(2) A speed reducer with rotation detector according to (1), wherein in case where the second shaft is held stationary and the first shaft is used as an output shaft, the code plate is supported by the first shaft, and the detecting portion is supported by the second shaft. Thereby, the code plate has typically the positional information recorded on the external peripheral face.
(3) The present invention provides a speed reducer with rotation detector according to (1) or (2), wherein the electronic device comprises multiplying means for multiplying the frequency of an electric signal which the detecting portion outputs. Thereby, the resolving power of the rotation detector is not limited to the resolving power of the code plate, but can be better than the resolving power of the code plate. Hence, the rotational information of one of the first shaft and the second shaft with respect to the other can be captured at high resolving power. Accordingly, if the speed reducer with rotation detector according to the invention is used with a motor, the rotational information output from the speed reducer with rotation detector can be detected. Thus, the rotation of the motor can be controlled at high resolving power, based on its information.
(4) A speed reducer with rotation detector according to (1) or (2), wherein the rotation detector has a plurality of detecting portions, and the electric device has removing means for removing the influence of the code plate due to eccentricity from the electric signal which the plurality of the detecting portions output. The speed reducer with rotation detector has a problem that the first shaft or the second shaft may be eccentric. Therefore, there is some possibility that the detecting portions cannot detect the rotational information of one of the first shaft and the second shaft with respect to the other correctly. Even if the electric signal output from the detecting portions is improved in precision, the rotational information of one of the first shaft and the second shaft with respect to the other may be low in precision. Thus, by providing the plurality of detecting portions, it is possible to provide the rotational information in which influence of eccentricity is removed from the rotational information detected by the detecting portions.
(5) A speed reducer with rotation detector according to (1) or (2), wherein the electric device comprises signal retention means for retaining an electric signal which the detecting portion outputs. Thereby, in a case where the code plate is an increment type, the code plate can be artificially made an absolute type because the signal retention means retains the electric signal output from the detector.
(6) A speed reducer with rotation detector according to (1) or (2), further comprising a seal interposed between the first shaft and the second shaft, wherein the seal partitions the space formed between the first shaft and the second shaft to prevent the foreign matter from sticking to the rotation detector. Thereby, it is possible to prevent the iron powder or friction power mixed into the oil within the speed reducer with rotation detector from sticking to the rotation detector and avoid degradation in the precision and resolving power of the rotation detector.
(7) a speed reducer with rotation detector according to (2), wherein the code plate has an external peripheral face with the positional information, and a first shaft mounting face formed co-axially with the external peripheral face and having the first shaft mounted uniaxially, and the first shaft has a rolling face for rolling the bearings, and a code plate mounting face formed co-axially with the rolling face on which the code plate is mounted uniaxially. Thereby, the recording center of positional information and the rotational center of the speed reducer with rotation detector can be made coincident. Therefore, the speed reducer with rotation detector according to the present invention can detect the output rotation at high precision.
(8) A speed reducer with rotation detector, including: an input shaft for inputting the rotation; a first shaft in co-axial relation with said input shaft, said first shaft having an integral first bearing rolling surface and a code plate; a second shaft in co-axial relation with said first shaft and surrounding one end portion of said first shaft to form a space with said first shaft, said second shaft having an integral second bearing rolling surface; a bearing that held between the first and second bearing rolling surface; a speed reducing mechanism that transmits rotation of said input shaft to said second shaft when said first shaft is held stationary; and a rotation detector that is accommodated in said space formed between the first shaft and the second shaft, and that detects information on relative rotation between said first and second shafts in cooperation with said code plate. Since the bearing rolling surface and the code plate are both provided on the common first shaft, the rotation can be detected with high accuracy.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 11-208971 (filed on Jul. 23, 1999), which is expressly incorporated herein by reference in its entirety.